UnderlinePageIndicator.java 文件源码

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    if (mViewPager == null) {
        return;
    }
    final int count = mViewPager.getAdapter().getCount();
    if (count == 0) {
        return;
    }

    if (mCurrentPage >= count) {
        setCurrentItem(count - 1);
        return;
    }

    final int paddingLeft = getPaddingLeft();
    final float pageWidth = (getWidth() - paddingLeft - getPaddingRight()) / (1f * count);
    final float left = paddingLeft + pageWidth * (mCurrentPage + mPositionOffset);
    final float right = left + pageWidth;
    final float top = getPaddingTop();
    final float bottom = getHeight() - getPaddingBottom();
    canvas.drawRect(left, top, right, bottom, mPaint);
}